The invention relates to a device for supplying ink to a line-type ink jet recording head having a plurality of nozzle openings arranged in a printing line direction.
Ink jet printers are extremely quiet compared to wire dot type printers and are less expensive to operate than thermal printers. However, ink jet printers, which jet ink droplets directly onto a recording medium, do not always produce high quality images because ink blots which occur on certain kinds of recording paper impair print quality. A thickener can be added to the ink in order to control blotting to some extent. The use of thickener, however, causes bubbles to stagnate in pressure producing chambers, insoluble substances to be deposited in pressure chambers and nozzles, nozzle openings to be clogged, etc., thus further deteriorating the performance of the printer.
On the other hand, to prevent the blots caused by directly jetting the ink onto the recording medium, a printer has been proposed in U.S. Pat. No. 4,538,156 which first transfers ink droplets onto a blot-free intermediate medium and thence to the recording paper a predetermined time after first receiving the jetted ink droplets on the blot-free intermediate medium.
If such a transfer technique is employed, recording can be made from the intermediate medium onto the recording paper after a solvent contained in the ink has been volatilized to some extent, thus allowing high quality prints to be obtained independently of the quality and type of recording paper.
However, the use of such a transfer technique extends the printing time because of the time required for printing on the intermediate medium. In addition, if the time difference between the printing of a first dot and the last dot on the intermediate medium becomes too long, the transfer performance becomes inconsistent due to large variations in the degree to which the solvent is dried. To overcome this problem, a line-type recording head having a plurality of nozzles arranged in the recording paper width direction to allow a line of data to be printed within a smallest possible time has been proposed.
However, ink used in the transfer type recording head must have an excellent film forming property and adhesiveness to maintain transferability relative to the recording paper after drying compared with ink used in a line type recording head which effects printing directly on the recording paper. Thus, bubbles are more likely to stagnate in pressure producing chambers, nozzle openings and other portions of the head. Stagnated bubbles can cause clogging and undesirable performance.
To eliminate nozzle clogging, a recording head has been proposed in Japanese Patent Unexamined Publication No. 123672/1984 in which common ink flow paths are arranged interposed between the pressure producing chambers, an ink supply inlet and an ink discharge outlet are disposed at one end of the ink flow paths, and a pressure difference is produced between the flow path points to circulate the ink in the pressure producing chambers.
Such ink circulation can prevent nozzle clogging to some extent, but if the length of the recording head is of the same order as the recording paper width, clogging of the nozzle opening remote from the ink supply inlet and the ink discharge outlet cannot be eliminated sufficiently.